Coated abrasive article

ABSTRACT

A coated abrasive article comprises a backing, a first binder on the backing, and a plurality of abrasive particles in the first binder. The first binder precursor is an energy-curable preferably, melt-processable resin containing an epoxy resin, an ethylene-vinyl acetate copolymer, and a curing agent for crosslinking the epoxy resin that is cured to provide a crosslinked make coating. The above binder precursors of the invention are preferably free of homopolymers and copolymers of olefinic monomers. In another aspect, the invention also describes an energy curable first binder precursor containing an epoxy resin, an ethylene-vinyl acetate copolymer, a polyfunctional acrylate component and a curing agent for crosslinking the epoxy resin that is cured to provide a crosslinked make coating. The invention also relates to a method of producing such coated abrasive articles and a surface-treated backing material.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/070,976, filed May 1, 1998, U.S. Pat. No. 6,077,601 which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to coated abrasive articles and moreparticularly, to such articles which incorporate energy curablecompositions containing an epoxy resin and an ethylene vinyl acetatecopolymer or an epoxy resin, an ethylene vinyl acetate copolymer and anacrylate.

BACKGROUND OF THE INVENTION

Coated abrasives generally comprise a flexible backing upon which abinder supports a coating of abrasive particles. The abrasive particlesare typically secured to the backing by a first binder, commonlyreferred to as a make coat. Additionally, the abrasive particles aregenerally oriented with their longest dimension perpendicular to thebacking to provide an optimum cut rate. A second binder, commonlyreferred to as a size coat, is then applied over the make coat and theabrasive particles to anchor the particles to the backing.

Porous cloth, fabric and textile materials are frequently used asbackings for coated abrasive articles. The make coat precursor istypically applied to the backing as a low viscosity material. In thiscondition, the make coat precursor can infiltrate into the intersticesof the porous backing leaving an insufficient coating thickness makingit difficult to bond the subsequently applied abrasive particles to thebacking and, on curing, resulting in the backing becoming stiff, hardand brittle. As a result, it has become conventional to employ one ormore treatment coats, such as a presize, saturant coat, backsize or asubsize coat, to seal the porous backing.

The presize, saturant coat, backsize and subsize coat typically involvethermally curable resinous adhesives, such as phenolic resins, epoxyresins, acrylate resins, acrylic latices, urethane resins, glue, starchand combinations thereof. A saturant coat saturates the cloth and fillspores, resulting in a less porous, stiffer cloth with more body. Anincrease in body provides an increase in strength and durability of thearticle. A presize coat, which is applied to the front side of thebacking, may add bulk to the cloth and may improve adhesion ofsubsequent coatings. A backsize coat, which is applied to the back sideof the backing, that is, the side opposite that to which the abrasivegrains are applied, adds body to the backing and protects the yams ofthe cloth from wear. A subsize coat is similar to a saturation coatexcept that it is applied to a previously treated backing. The drawbackof such a presize, saturant coat, backsize and subsize coat is that itentails added processing step(s) which increase the cost and complexityof manufacturing. Similarly, paper backings may be treated to preventpenetration of make adhesives and/or to waterproof.

SUMMARY OF THE INVENTION

This invention generally relates to a coated abrasive article utilizingan improved make coat formulation. The coated abrasive article includesa backing, the improved make coat on the backing, and a plurality ofabrasive particles at least partially embedded in the make coat. Themake coat also may be referred to herein as the first binder.

The present invention provides a coated abrasive article, comprising:

a) a backing having a front surface and a back surface;

b) a crosslinked first binder on said front surface of said backing,

wherein said first binder is formed from a first binder precursor, saidfirst binder precursor is an energy-curable composition made by mixingthe following components

i) about 2 to about 99 weight percent of an epoxy resin, the weightpercent being based on the total resin content;

ii) about 1 to about 98 weight percent of an ethylene-vinyl acetatecopolymer resin, the weight percent being based on the total resincontent;

iii) an effective amount of a curing agent for crosslinking said epoxyresin; and

c) a plurality of abrasive particles, wherein said abrasive particlesare at least partially embedded in said first binder.

The above binder precursor compositions of the invention are homogeneousin the molten state and are preferably free from, that is, do notcontain, hydrocarbon polyolefin resins. “Hydrocarbon polyolefm resin”refers to a fully prepolymerized uncrosslinked polymeric hydrocarbonbearing essentially no organic functional groups, prepared fromhomopolymerization and/or copolymerization of an olefinic monomer(s).Such resins can be incompatible with epoxy resins and can cause phaseseparation of compositions containing an appreciable amount of epoxyresin. Examples of such resins include polyethylene, polypropylene, andthe like, and poly(ethylene-co-propylene), poly(propylene-co-1-butene),and the like.

In another aspect, the present invention provides a coated abrasivearticle, comprising:

a) a backing having a front surface and a back surface;

b) a crosslinked fist binder on said front surface of said backing,

wherein said first binder is formed from a first binder precursor, saidfirst binder precursor is an energy-curable composition made by mixingthe following components

i) about 2 to about 98 weight percent of an epoxy resin, the weightpercent being based on the total resin content;

ii) about 1 to about 90 weight percent of an ethylene-vinyl acetatecopolymer resin, the weight percent being based on the total resincontent;

iii) about 0.1 to about 20 weight percent of a polyfunctional acrylate,the weight percent being based on the total resin content;

iv) an effective amount of a curing agent for crosslinking said epoxyresin; and

c) a plurality of abrasive particles, wherein said abrasive particlesare at least partially embedded in said first binder.

In another aspect, the present invention provides an energy-curablecomposition made by mixing components comprising:

a) an epoxy resin;

b) an ethylene-vinyl acetate copolymer resin;

c) a polyfunctional acrylate; and

d) an effective amount of a curing agent for crosslinking said epoxyresin.

In another aspect, the present invention provides a presized backing fora coated abrasive article comprising:

a) a backing suitable for use in a coated abrasive article; and

b) a crosslinked presize layer on the backing formed from a presizebinder precursor, wherein the presize binder precursor is an energycurable composition comprising:

i) from about 30 to about 95 weight percent of an epoxy resin, theweight percent being based on the total resin content,

ii) from about 5 to about 70 weight percent an ethylene-vinyl acetatecopolymer resin, the weight percent being based on the total resincontent, and

iii) an effective amount of a curing agent for crosslinking said epoxyresin.

In another aspect, the present invention provides a presized backing fora coated abrasive article comprising:

a) a backing suitable for use in a coated abrasive article; and

b) a crosslinked presize layer on the backing formed from a presizebinder precursor, wherein the presize binder precursor is an energycurable composition comprising:

i) about 2 to about 98 weight percent of an epoxy resin, the weightpercent being based on the total resin content,

ii) about 1 to about 90 weight percent of an ethylene-vinyl acetatecopolymer resin, the weight percent being based on the total resincontent,

iii) about 0.1 to about 20 weight percent of a polyfunctional acrylatecomponent, the weight percent being based on the total resin content,and

iv) an effective amount of a curing agent for crosslinking said epoxyresin.

The above binder precursors of the invention are preferably meltprocessable.

As used herein, a “hot melt” refers to a composition that is a solid atroom temperature (about 20 to 22° C.) but which, upon heating, melts toa viscous liquid that can be readily applied to a coated abrasivearticle backing. A “melt processable” composition refers to acomposition that can transform, for example, by heat and/or pressure,from a solid to a viscous liquid by melting, at which point it can bereadily applied to a coated abrasive article backing. Both hot melt andmelt processable resin compositions can be in the form of a solid filmthat is transfer coated to the backing. Desirably, the hot meltcompositions of the invention can be formulated as solvent free systems(that is, they have less than 1% solvent in the solid state).

However if so desired, it may be feasible to incorporate solvent orother volatiles into the binder precursor. As used herein, a “pressuresensitive adhesive” refers to a hot melt composition that, at the timeabrasive particles are applied thereto, displays pressure sensitiveadhesive properties. “Pressure sensitive adhesive properties” means thatthe composition is tacky immediately after application to a backing andwhile still warm and, in some cases, even after it has cooled to roomtemperature. “EVA” means ethylene-vinyl acetate copolymer and “epoxy”means epoxide containing material or epoxy resin.

In a further embodiment of the present invention, a size coat, that is,a second binder, can be applied upon the make coat and abrasiveparticles to reinforce the attachment of the abrasive particles to thebacking. A supersize coat, that is, a third binder, over the size coat,also may be used.

The make coat precursor or binder precursor may be in a solid form priorto coating and can be coated as a liquid solution or a molten mixture.

The invention additionally relates to use of the preferably energycurable, hot melt pressure sensitive first binder as a backing treatmentcoating for porous cloth materials to function, for example, as asaturant coat, a presize coat, a backsize coat, or as a subsize coat, toprotect the cloth fibers and/or to seal the porous cloth material. Ifliquefied, the binder precursor can be coated as a size coat.Preferably, any backing treatment applied to the coatable side of thebacking, for example, presize, is cured or crosslinked before aprecursor and abrasive particles are applied to the treated surface ofthe backing. The cured coating or treatment on the backing is preferablysubstantially free of abrasive particles.

The binder precursors of the present invention also generally have alonger open time, better film-forming properties (which allows forformulating at lower levels), and lower cost than polyester/epoxy meltprocessable make resins. The binder precursors of the invention alsohave significant tack in the uncured state, controlled flow duringcuring, and desirable physical properties in the cured state, includingadhesive and cohesive strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged sectional view of a segment of a coated abrasivearticle according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, FIG. 1 illustrates a coated abrasivearticle 10 according to the invention comprising a backing 12 and anabrasive layer 14 bonded thereto.

Backing 12 may be a conventional, sealed coated abrasive backing or aporous, non-sealed backing. Backing 12 may be comprised of cloth,vulcanized fiber, paper, nonwoven materials, fibrous reinforcedthermoplastic backing, substrates containing hooked stems, loopedfabrics, metal foils, mesh, foam backings, and laminated multilayercombinations thereof.

Cloth backings can be untreated, saturated, pre-sized, backsized,porous, or sealed, and they may be woven or stitch bonded. The clothbackings may include fibers or yarns of cotton, polyester, rayon, silk,nylon or blends thereof. The cloth backings can be provided as laminateswith different backing materials described herein.

Paper backings also can be saturated, barrier coated, pre-sized,backsized, untreated, or fiber-reinforced. The paper backings also canbe provided as laminates with a different type of backing material.Nonwoven backings include scrims and laminates to different backingmaterials mentioned herein. The nonwovens may be formed of cellulosicfibers, synthetic fibers or blends thereof. The backing can also be astem web used alone or incorporating a nonwoven, or as a laminate with adifferent type of backing.

The loop fabric backing can be brushed nylon, brushed polyester,polyester stitched loop, and loop material laminated to a different typeof backing material. The foam backing may be a natural sponge materialor polyurethane foam and the like.

The foam backing also can be laminated to a different type of backingmaterial. The mesh backings can be made of polymeric or metal open-weavescrims. Additionally, the backing may be a spliceless belt such as thatdisclosed in U.S. Pat. Nos. 5,573,619, 5,609,706, and 5,681,612(Benedict et al.), or a reinforced thermoplastic backing that isdisclosed in U.S. Pat. No. 5,417,726 (Stout et al.).

Abrasive layer 14 comprises a multiplicity of abrasive particles 16which are bonded to a major surface of backing 12 by a first binder ormake coat 18. A second binder or size coat 20 is applied over theabrasive particles and the make coat to reinforce the particles. Theabrasive particles typically have an average diameter of about 0.1 to1500 microns (μm), more preferably from about 1 to 1300 μm. Examples ofuseful abrasive particles include fused aluminum oxide based materialssuch as aluminum oxide, ceramic aluminum oxide (which may include one ormore metal oxide modifiers and/or seeding or nucleating agents), andheat treated aluminum oxide, silicon carbide, co-fused alumina-zirconia,diamond, ceria, titanium diboride, cubic boron nitride, boron carbide,garnet and blends thereof. Abrasive particles also include abrasiveagglomerates such as disclosed in U.S. Pat. No. 4,652,275 and U.S. Pat.No. 4,799,939, incorporated by reference herein.

The first binder is formed from a first binder precursor. The term“precursor” means the binder is uncured and not crosslinked. The term“crosslinked” means a material having polymeric sections that areinterconnected through chemical bonds (that is, interchain links) toform a three-dimensional molecular network. Thus, the first binderprecursor is in an uncured state when applied to the backing. Ingeneral, the first binder comprises a cured or crosslinked thermosettingpolymer. For purposes of this application, “cured” and “polymerized” canbe used interchangeably. However, with the appropriate processingconditions and catalysts, the first binder precursor is capable ofcrosslinking to form a thermosetting binder. For purposes of thisinvention, the first binder precursor is “energy-curable”, “curable” or“uncured” in the sense that it can crosslink (that is, cures) uponexposure to radiation, for example, actinic radiation, electron beamradiation, and/or thermal radiation.

Additionally, under the appropriate processing conditions, the firstbinder precursor is a hot melt pressure sensitive adhesive. For example,depending upon the chemistry, at room temperature the first binderprecursor may be a solid. For instance, the first binder precursor maybe a solid film that is transfer coated to the backing. Upon heating toelevated temperature, this first binder precursor is capable of flowing,increasing the tack of the hot melt pressure sensitive adhesive.Altematively, for instance, if the resin is solvent-borne, the firstbinder precursor may be liquid at room temperature.

In one embodiment of the invention, first binder precursors useful inthe make coat formulations of the coated abrasive articles of theinvention preferably include a hot melt pressure sensitive adhesivecomposition that cures upon exposure to energy to provide a covalentlycrosslinked, thermoset make coat. Because the first binder precursor canbe applied as a hot melt composition, with the appropriate processingconditions, the first binder precursor does not readily penetrate thebacking so as to compromise the backing's inherent pliability andflexibility. Consequently, the binder precursors disclosed herein areparticularly advantageous when employed in conjunction with porouscloth, fabric or textile backings. However, the first binder precursorwill penetrate into the backing to some degree to provide good adhesionto the backing. This degree of penetration will depend in part on theparticular chemistry and processing conditions, and can be controlled.

The term “porous” as used herein in connection with backings, means abacking not having an abrasive layer, a make coat, an adhesive layer, asealant, a saturant coat, a presize coat, a backsize coat, and so forththereon, and which demonstrates a Gurley porosity of less than 50seconds when measured according to Federal Test Method Std. No. 191,Method 5452 (published Dec. 31, 1968) (as referred to in the WellingtonSears Handbook of Industrial Textiles by E. R. Kaswell, 1963 edition,page 575) using a Gurley Permeometer (available from Teledyne Gurley,Inc., Troy, N.Y.). Cloth backings of presently known coated abrasivearticles conventionally require special treatments such as a saturantcoat, a presize coat, a backsize coat or a subsize coat to protect thecloth fibers and to seal the backing. The backing may be free of thesetreatments. Alternatively, the backing may comprise one or more of thesetreatments. The type of backing and backing treatment depends in part onthe desired properties for the intended use. The hot melt make coats ofthe invention can provide such treatments.

The pressure sensitive adhesive qualities of the uncured hot melt makecoat enable the abrasive particles to adhere to the uncured make coatprior to the curing process. The crosslinked, thermoset make coat istough, yet flexible, and aggressively adheres to the backing.

The binder precursors useful in the invention include an epoxy resinthat contributes to the toughness and durability of the cured make coat,a thermoplastic that allows for the uncured make coat to displaypressure sensitive adhesive properties and preferably, consistingessentially of an ethylene-vinyl acetate copolymer (EVA), and a catalystfor the epoxy portion of the make coat formulation. Optionally, thebinder precursors of the invention may also include a thermoplasticpolyester to provide additional pressure sensitive adhesive propertiesand to compatibilize the EVA and epoxy resins, a hydroxyl-containingmaterial to modify the rate of curing and/or stiffness of the makecoats, a tackifier, a filler, and the like.

Preferred binder precursors of the invention contain from about 45 toabout 95 weight percent epoxy resin and from about 5 to about 55 weightpercent of ethylene-vinyl acetate copolymer, the weight percent beingbased on the total resin content. A more preferred binder precursorcontains from about 70 to about 95 weight percent of epoxy resin andfrom about 5 to about 30 weight percent ethylene-vinyl acetate copolymerand contain no hydroxyl containing material, the weight percent beingbased on the total resin content.

Other preferred binder precursors of the invention contain from about 50to about 94 weight percent epoxy resin, from about 5 to about 50 weightpercent of ethylene-vinyl acetate copolymer, and from about 0.1 to about15 weight percent of polyfunctional acrylate component, the weightpercent being based on the total resin content. Other more preferredbinder precursors of the invention contain from about 70 to about 92weight percent epoxy resin, from about 5 to about 30 weight percentethylene-vinyl acetate copolymer, and from about 3 to about 15 weightpercent of a polyfunctional acrylate component, the weight percent beingbased on the total resin content. “Total resin content” means the sum ofepoxy resin, EVA copolymer, and polyacrylate component, if present.

Epoxy Resins

Epoxy resins useful in the adhesive compositions of the invention areany organic compounds having at least one oxirane ring, that is,

polymerizable by a ring opening reaction. Such materials, broadly calledepoxides, include both monomeric and polymeric epoxides and can bealiphatic, alicyclic, heterocyclic, cycloaliphatic, or aromatic and canbe combinations thereof. They can be liquid or solid or blends thereof,blends being useful in providing tacky adhesive films. These materialsgenerally have, on the average, at least two epoxy groups per moleculeand are also called “polyepoxides.” The polymeric epoxides includelinear polymers having terminal epoxy groups (for example, a diglycidylether of a polyoxyalkylene glycol), polymers having skeletal oxiraneunits (for example, polybutadiene polyepoxide), and polymers havingpendent epoxy groups (for example, a glycidyl methacrylate polymer orcopolymer). The molecular weight of the epoxy resin may vary from about74 to about 100,000 or more. Mixtures of various epoxy resins can alsobe used in the hot melt compositions of the invention. The “average”number of epoxy groups per molecule is defined as the number of epoxygroups in the epoxy resin divided by the total number of epoxy moleculespresent.

Useful epoxy resins include those which contain cyclohexene oxide groupssuch as the epoxycyclohexane carboxylates, typified by3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For amore detailed list of useful epoxides of this nature, reference may bemade to U.S. Pat. No. 3,117,099, incorporated herein by reference.

Further epoxy resins which are particularly useful in the practice ofthis invention include glycidyl ether monomers of the formula:

Where R′ is aliphatic(for example, alkyl), aromatic (for example, aryl),or combinations thereof, and n is an integer of 1 to 6. Examples are theglycidyl ethers of polyhydric phenols obtained by reacting a polyhydricphenol with an excess of chlorohydrin such as epichlorohydrin, forexample, the diglycidyl ether of 2,2-bis-(4-hydroxyphenyl)propane(Bisphenol A). Further examples of epoxides of this type which can beused in the practice of this invention are described in U.S. Pat. No.3,018,262, incorporated herein by reference. Preferred epoxy resinsinclude the diglycidyl ethers of Bisphenol A.

There is a host of commercially available epoxy resins which can be usedin this invention. In particular, epoxides which are readily availableinclude octadecylene oxide, epichlorohydrin, styrene oxide,vinylcyclohexene oxide, glycidyl methacrylate, diglycidyl ether ofBisphenol A (for example, those available under the trade designations“EPON 828,”“EPON 1004,” and “EPON 1001F” from Shell Chemical Co.,Houston, Tex., and “DER-332” and “DER-334,” from Dow Chemical Co.,Midland, Mich.), diglycidyl ether of Bisphenol F (for example, thoseunder the trade designations “ARALDITE GY281” from Ciba-Geigy Corp.,Hawthorne, N.Y., and “EPON 862” from Shell Chemical Co.),vinylcyclohexene dioxide (for example, having the trade designation “ERL4206” from Union Carbide Corp., Danbury, Conn.),3,4-epoxycyclohexyl-methyl-3,4-epoxycyclohexene carboxylate (forexample, having the trade designation “ERL-4221” from Union CarbideCorp.), 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-metadioxane (for example, having the trade designation“ERL-4234” from Union Carbide Corp.), bis(3,4-epoxycyclohexyl) adipate(for example, having the trade designation “ERL-4299” from Union CarbideCorp.), dipentene dioxide (for example, having the trade designation“ERL-4269” from Union Carbide Corp.), epoxidized polybutadiene (forexample, having the trade designation “OXIRON 2001” from FMC Corp.),epoxy silanes, for example,beta-3,4-epoxycyclohexylethyltrimethoxysilane andgamma-glycidoxypropyltrimethoxysilane, commercially available from UnionCarbide, flame retardant epoxy resins (for example, having the tradedesignation “DER-542,” a brominated bisphenol type epoxy resin availablefrom Dow Chemical Co.), 1,4-butanediol diglycidyl ether (for example,having the trade designation “ARALDITE RD-2” from Ciba-Geigy Corp.),hydrogenated bisphenol A-epichlorohydrin based epoxy resins (for examplehaving the trade designation “EPONEX 1510” from Shell Chemical Co.), andpolyglycidyl ethers of phenol-formaldehyde novolaks (for example, havingthe trade designation “DEN-431” and “DEN-438” from Dow Chemical Co.).

Ethylene Vinyl Acetate Copolymer

The thermoplastic component of the binder precursors and make resins ofthe invention includes and preferably, consists essentially of one ormore thermoplastic ethylene-vinyl acetate copolymer resins. Ethylenevinyl acetate (“EVA”) copolymers are well known, and may be prepared byhigh pressure free radical copolymerization of vinyl acetate andethylene as is known in the art. Useful EVA copolymers include thosehaving a vinyl acetate moiety content of not less than about 30%,generally, not less than about 40%, preferably, not less than about 50%,and even more preferably, not less than about 60% by weight of thecopolymer. Useful EVA copolymers also include those having a vinylacetate content in the range of from about 20 to about 99%, preferably,from about 40 to about 95%, more preferably from about 50 to about 90%,and even more preferably from about 60 to about 80% by weight of thecopolymer.

There are many commercial sources for EVA copolymers such as, forexample, E. I. Du Pont de Nemours and Co. (Wilmington, Del.) under thetrade designation “ELVAX”, Bayer Corp. (Pittsburgh, Pa.) under the tradedesignation “LEVAPREN”, and AT Plastics, Inc. (Ontario, Canada).

Non-limiting examples of commercially available EVA copolymers that maybe used in practice of the present invention include AT Plastics 3325MEVA copolymer (33 weight percent vinyl acetate); ELVAX™ 40W andLEVAPREN™ 400 (40 weight percent vinyl acetate); LEVAPREN™ 450, 452 and456(45 weight percent vinyl acetate); LEVAPREN™ 500 HV (50 weightpercent vinyl acetate); LEVAPREN™ 600 HV (60 weight percent vinylacetate); and LEVAPREN™ 700 HV (70 weight percent vinyl acetate).

The components used to form the binder precursor compositions of theinvention that contain epoxy resin and EVA are compatible in the moltenstate. “Compatible” means that the molten mixture of at least the epoxyresin and the thermoplastic components is single phased, that is, doesnot visibly phase separate among the individual components and forms ahomogeneous mixture of molten components. Of course, one skilled in theart can easily vary the concentrations of the epoxy resins, EVAcopolymers and vinyl acetate content therein, and catalysts to formhomogeneous compositions of the invention without undue experimentation.For example, one skilled in the art would generally increase the vinylacetate concentration of the EVA copolymer as the concentration of epoxyresin in the uncured composition increases so to maintain a singledphased composition in the molten state.

The specific physical properties of the cured binder containing epoxyresin and EVA may also be tailored to suit the specific application byadjusting the ratio of the preceding components. Generally, increasedtack and adhesion to high energy surfaces, and a decreased tendency toflow during cure is achieved by increasing the relative amount of EVAcopolymer in the formulation. Additionally, tack of the composition maybe affected by the amount of plasticization of the EVA copolymer by aliquid epoxy resin. The amount of photocatalyst is selected to optimizecure speed and uniformity of through cure. Thus, the relative amounts ofthe above-mentioned ingredients are balanced depending on the propertiessought in the final composition.

Polyfunctional Acrylate

A “polyfunctional acrylate” component of one embodiment of the binderprecursor compositions of the invention means ester compounds which arethe reaction product of aliphatic polyhydroxy compounds and(meth)acrylic acids. The aliphatic polyhydroxy compounds includecompounds such as (poly)alkylene glycols and (poly)glycerols.

(Meth)acrylic acids are unsaturated carboxylic acids which include, forexample, those represented by the following basic formula:

where R is a hydrogen atom or a methyl group.

Polyfunctional acrylates can be a monomer or an oligomer. For purposesof this invention, the term “monomer” means a small(low-molecular-weight) molecule with an inherent capability of formingchemical bonds with the same or other monomers in such manner that longchains (polymeric chains or macromolecules) are formed. For thisapplication, the term “oligomer” means a polymer molecule having 2 to 10repeating units (for example, dimer, trimer, tetramer, and so forth)having an inherent capability of forming chemical bonds with the same orother oligomers in such manner that longer polymeric chains can beformed therefrom. Mixtures of monomers and oligomers also could be usedas the polyfunctional acrylate component. It is preferred that thepolyfunctional acrylate component be monomeric.

Representative polyfunctional acrylate monomers include, by way ofexample and not limitation: ethylene glycol diacrylate, ethylene glycoldimethacrylate, hexanediol diacrylate, triethylene glycol diacrylate,trimethylolpropane triacrylate, ethoxylated trimethylolpropanetriacrylate, glycerol triacrylate, pentaerthyitol triacrylate,pentaeryflritol trimethacrylate, pentaerythritol tetraacrylate,pentaerytlritol tetunethacrylate, and neopentylglycol diacrylate.Mixtures and combinations of different types of such polyfunctionalacrylates also can be used. The term “acrylate”, as used herein,encompasses acrylates and methacrylates.

Useful commercially available polyfunctional acrylates includetrimethylolpropane triacrylate having the trade designation “SR351,”ethoxylated trimethylolpropane triacrylate having the trade designation“SR454,” pentaerytlritol tetraacrylate having the trade designation“SR295,” and neopentylglycol diacrylate having the trade designation“SR247,” all available from Sartomer Co., Exton, Pa.

The polyfunctional acrylate monomers cure quickly into a network due tothe multiple functionalities available on each monomer. If there is onlyone acrylate functionality, a linear, non-networked molecule will resultupon cure of the material. Polyfunctional acrylates having afunctionality of two or more are preferred in this invention toencourage and promote the desired polymeric network formation.

Useful polyfunctional acrylate oligomers include commercially availablepolyether oligomers such as polyethylene glycol 200 diacrylate havingthe trade designation “SR259” and polyethylene glycol 400 diacrylatehaving the trade designation “SR344,” both available from Sartomer Co.,Exton, Pa.

Other oligomers include acrylated epoxies such as diacrylated esters ofepoxy resins, for example, diacrylated esters of bisphenol A epoxyresin. Examples of commercially available acrylated epoxies includeepoxies available under the trade designations “EBECRYL 3500,” “EBECRYL3600,” and “EBECRYL 3700,” from UCB Chemicals Corp., Smyrna, Ga.

In general, the optimal amount of the polyfunctional acrylate used inthe binder precursor composition is proportional to the acrylateequivalent weight and inversely proportional to the acrylatefunctionality.

Binder precursor compositions based on epoxy and ethylene-vinyl acetatecopolymer which also contain the polyfunctional acrylates are alsohigher in viscosity after exposure to UV radiation. This feature allowsfor a fine-tuning of the relative rates of epoxy cure and resin flowallowing for control of the degree of abrasive particle wetting andorientation. As general formulation guidelines, with too littlepolyfunctional acrylate, the binder precursor can flow too readily,wetting the abrasive particles so well that the abrasive particles areburied below the surface of the coating, particularly with thickercoatings.

With too much polyfunctional acrylate, the binder precursor cannot flowsufficiently to wet the abrasive particles before the epoxy component isfully cured. In this case, even though the uncured binder resin isaggressively tacky at room temperature, abrasive particle adhesion ispoor because wetting is precluded by the rheology of the post-irradiatedresin. On the other hand, increasing amounts of the epoxy resin relativeto the ethylene-vinyl acetate component and polyfunctional acrylatecomponent tends to result in stiffer cured binders. Thus, the relativeamounts of these three ingredients are balanced depending on theproperties sought in the final binder.

Catalysts

Catalysts of the present invention preferably can be activated byphotochemical means, such as by actinic radiation (radiation having awavelength in the ultraviolet or visible portion of the electromagneticspectrum). Useful photocatalysts are of two general types: onium saltsand cationic organometallic salts, both described in U.S. Pat. No.5,709,948, incorporated herein by reference.

Onium salt photoinitiators for cationic polymerizations include iodoniumand sulfonium complex salts. Useful aromatic iodonium complex salts areof the general formula:

wherein

Ar¹ and Ar² can be the same or different and are aromatic groups havingfrom 4 to about 20 carbon atoms, and are selected from the groupconsisting of phenyl, thienyl, furanyl, and pyrazolyl groups;

Z is selected from the group consisting of oxygen, sulfur, nitrogen, acarbon-carbon bond,

wherein R can be aryl (having from 6 to about 20 carbon atoms, such asphenyl) or acyl (having from 2 to about 20 carbon atoms, such as acetyl,or benzoyl), and

wherein R₁ and R₂ are selected from the group consisting of hydrogen,alkyl radicals having from 1 to about 4 carbon atoms, and alkenylradicals having from 2 to about 4 carbon atoms;

m is zero or 1; and

X has the formula DQ_(n), wherein D is a metal from Groups IB to VIII ora metalloid from Groups IIIA to VA of the Periodic Chart of the Elements(Chemical Abstracts version), Q is a halogen atom, and n is an integerhaving a value of from 1 to 6. Preferably, the metals are copper, zinc,titanium, vanadium, chromium, magnesium, manganese, iron, cobalt, ornickel and the metalloids preferably are boron, aluminum, antimony, tin,arsenic and phosphorous. Preferably, the halogen, Q, is chlorine orfluorine. Illustrative of suitable anions are BF₄ ⁻, PF₆ ⁻, SbF₆ ⁻,FeCl₄ ⁻, SnCl₅ ⁻, AsF₆ ⁻, SbF₅OH⁻, SbCl₆ ⁻, SbF₅ ⁻², AlF₅ ⁻², GaCl₄ ⁻,InF₄ ⁻, TiF₆ ⁻², ZrF₆ ⁻², CF₃SO₃ ⁻ and the like. Preferably, the anionsare BF₄ ⁻, PF₆ ⁻, SbF₆ ⁻, AsF₆ ⁻, SbF₅OH⁻, and SbCl₆ ⁻. More preferably,the anions are SbF₆ ⁻, AsF₆ ⁻, and SbF₅OH⁻.

The Ar₁ and Ar₂ aromatic groups may optionally comprise one or morefused benzo rings (for example, naphthyl, benzothienyl, dibenzothienyl,benzofuranyl, dibenzofiranyl, etc.). The aromatic groups may also besubstituted, if desired, by one or more non-basic groups if they areessentially non-reactive with epoxide and hydroxyl functionalities.

Useful aromatic iodonium complex salts are described more fully in U.S.Pat. No. 4,256,828, which is incorporated herein by reference. Thepreferred aromatic iodonium complex salts are (Ar)₂I PF₆ and (Ar)₂ISbF₆.

The aromatic iodonium complex salts usefuil in the invention arephotosensitive only in the ultraviolet region of the spectrum. However,they can be sensitized to the near ultraviolet and the visible range ofthe spectrum by sensitizers for known photolyzable organic halogencompounds. Illustrative sensitizers include aromatic amines and coloredaromatic polycyclic hydrocarbons, as described in U.S. Pat. No.4,250,053, incorporated herein by reference.

Aromatic sulfonium complex salt initiators suitable for use in theinvention are of the general formula

wherein

R₃, R₄ and R₅ can be the same or different, provided that at least oneof the groups is aromatic. These groups can be selected from the groupconsisting of aromatic moieties having from 4 to about 20 carbon atoms(for example, substituted and unsubstituted phenyl, thienyl, andfuranyl) and alkyl radicals having from 1 to about 20 carbon atoms. Theterm “alkyl” includes substituted alkyl radicals (for example,substituents such as halogen, hydroxy, alkoxy, and aryl). Preferably,R₃, R₄ and R₅ are each aromatic; and

Z, m and X are all as defined above with regard to the iodonium complexsalts.

If R₃, R₄ or R₅ is an aromatic group, it may optionally have one or morefused benzo rings (for example, naphthyl, benzothienyl, dibenzothienyl,benzofuranyl, dibenzofliranyl, etc.). The aromatic groups may also besubstituted, if desired, by one or more non-basic groups if they areessentially non-reactive with epoxide and hydroxyl functionalities.

Triaryl-substituted salts such as triphenylsulfoniumhexafluoroantimonate and p-(henyl(thiophenyl)diphenylsulfoniumhexafluoroantimonate are the preferred sulfonium salts. Useful sulfoniumsalts are described more fully in U.S. Pat. No. 5,256,828.

Aromatic sulfoni-um complex salts useful in the invention arephotosensitive only in the ultraviolet region of the spectrum. However,they can be sensitized to the near ultraviolet and the visible range ofthe spectrum by a select group of sensitizers such as described in U.S.Pat. Nos. 4,256,828 and 4,250,053.

Suitable photoactivatable organometallic complex salts useful in theinvention include those described in U.S. Pat. Nos. 5,059,701,5,191,101, and 5,252,694, each of which is incorporated herein byreference. Such salts of organometallic cations have the generalformula:

[(L¹)(L²)M^(m)]^(+e)X⁻

wherein

M^(m) represents a metal atom selected from elements of periodic groupsIVB, VB, VIB, VIIB and VIII, preferably Cr, Mo, W, Mn, Re, Fe, and Co;

L¹ represents none, one, or two ligands contributing π-electrons thatcan be the same or different ligand selected from the group consistingof substituted and unsubstituted alicyclic and cyclic unsaturatedcompounds and groups and substituted and unsubstituted carbocyclicaromatic and heterocyclic aromatic compounds, each capable ofcontributing two to twelve α-electrons to the valence shell of the metalatom M. Preferably, L¹ is selected from the group consisting ofsubstituted and unsubstituted η³-allyl, η⁵-cyclopentadienyl,η⁷-cycloheptatrienyl compounds, and η⁶-aromatic compounds selected fromthe group consisting of η⁶-benzene and substituted η⁶-benzene compounds(for example, xylenes) and compounds having 2 to 4 fused rings, eachcapable of contributing 3 to 8 π-electrons to the valence shell ofM^(m);

L² represents none or 1 to 3 ligands contributing an even number ofπ-electrons that can be the same or different ligand selected from thegroup consisting of carbon monoxide, nitrosonium, triphenyl phosphine,triphenyl stibine and derivatives of phosphorous, arsenic and antimony,with the proviso that the total electronic charge contributed to M^(m)by L¹ and L² results in a net residual positive charge of e to thecomplex; and

e is an integer having a value of 1 or 2, the residual charge of thecomplex cation;

X is a halogen-containing complex anion, as described above.

Examples of suitable salts of organometallic complex cations useful asphotoactivatable catalysts in the present invention include:

(η⁶-benzene)(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻

(η⁶-toluene)(η⁵-cyclopentadienyl)Fe⁺¹AsF₆ ⁻

(η⁶-xylene)(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻

(η⁶-cumene)(η⁵-cyclopentadienyl)Fe⁺¹PF₆ ⁻

(η⁶-xylenes (mixed isomers))(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻

(η⁶-xylenes (mixed isomers))(η⁵-cyclopentadienyl)Fe⁺¹PF₆ ⁻

(η⁶-o-xylene)(η⁵-cyclopentadienyl)Fe⁺¹CF₃SO₃ ⁻

(η⁶-m-xylene)(η⁵-cyclopentadienyl)Fe⁺¹BF₄ ⁻

(η⁶-mesityene)(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻

(η⁶-hexamethylbenzene)(η⁵-cyclopentadienyl)Fe⁺¹SbF₅OH⁻ and

(η⁶-fluorene)(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻.

Preferred salts of organometallic complex cations useful in theinvention include one or more of the following: (η⁶-xylenes (mixedisomers))(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻, (η⁶-xylenes (mixedisomers))(η⁵-cyclopentadienyl)Fe⁺¹PF₆ ⁻,(η⁶-xylene)(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻, and(η⁶-mesitylene)(η⁵-cyclopentadienyl)Fe⁺¹SbF₆ ⁻.

Useful commercially available initiators include FX-512™ (MinnesotaMining and Manufacturing Company, St Paul, Minn.), CD-1010™ and CD-1012™(Sartomer, Exton, Pa.) aromatic sulfonium complex salts, UVI™-6974, anaromatic sulfonium complex salt (Union Carbide Corp., Danbury, Conn.)and IRGACURE™ 261, a cationic organometallic complex salt (Ciba GeigyChemicals, Hawthorne, N.Y.).

Preferably, the photocatalyst of the invention if employed comprisesfrom about 0.01 to about 10 weight percent, more preferably from 0.1 toabout 5 weight percent, still more preferably from about 0.5 to about 2weight percent of a photocatalyst based on the total weight of the resinpresent in the composition.

Where the catalytic photoinitiator used for curing the epoxy resin is ametallocene salt catalyst, it preferably is accompanied by anaccelerator such as an oxalate ester of a tertiary alcohol as describedin U.S. Pat. No. 5,436,063, although this is optional. Oxalateco-catalysts that can be used include those described in U.S. Pat. No.5,252,694. The accelerator preferably comprises from about 0.1 to about4% of the binder composition based on the combined weight of the epoxyresin, and the ethylene-vinyl acetate copolymer.

Although the preferred curing agent for epoxy resins is a cationicphotocatalyst, certain thermally-activated curing agents for epoxyresins (for example, compounds that effect curing and crosslinking ofthe epoxide by entering into a chemical reaction therewith) are usefulin the present invention. Preferably, such curing agents are thermallystable at temperatures at which mixing of the components takes place.

Suitable thermal curing agents include aliphatic and aromatic primaryand secondary amines, for example, di(4-aminophenyl)sulfone,di(4-aminophenyl)ether, and 2,2-bis-(4-aminophenyl)propane; aliphaticand aromatic tertiary amines, for example, dimethylaminopropylamine;fluorene diamines, such as those described in U.S. Pat. No. 4,684,678,incorporated herein by reference; boron trifluoride complexes such asBF₃Et₂O and BF₃H₂NC₂H₄OH; imidazoles, such as methylimidazole;hydrazines, such as adipohydrazine; and guanidines, such astetramethylguanidine and dicyandiamide (cyanoguanidine, also commonlyknown as DiCy), and mixtures thereof.

Useful commercially available thermal curing agents include AMICURE™CG-1200, dicyandiamide (Air Products and Chemicals, Allentown, Pa.), andCUREZOL™ 2MZ-AZINE,2,4-diamino-6(2′methylimidazoleyl-(1′))ethyl-s-triazine (Air Productsand Chemicals).

Preferably, the thermal curative of the invention comprises from about 1to 25 weight percent, more preferably from about 2 to about 20 weightpercent, and still more preferably from about 3 to about 15 weightpercent of one or more thermal catalysts, the weight percent being basedon the combined weight of the epoxy resin, ethylene-vinyl acetatecomponent, and the polyfunctional acrylate component, if present.

In the case of the free radical curable polyfunctional acrylatecomponent, it is useful to add a free radical initiator to the make coatprecursor, although it should be understood that an electron beam sourcealso could be used to initiate and generate free radicals. The freeradical initiator preferably is added in an amount of 0.1 to 3.0% byweight, based on the total amount of resinous components.

Examples of useful photoinitiators, that generate a free radical sourcewhen exposed to ultraviolet light, include, but are not limited to,organic peroxides, azo compounds, quinones, benzophenones, nitrosocompounds, acyl halides, hydrazones, mercapto compounds, pyryliumcompounds, triacylimidazoles, acylphosphine oxides, bisimidazoles,chloroalkyltriazines, benzoin ethers, benzil ketals, thioxanthones, andacetophenone derivatives, and mixtures thereof.

Examples of photoinitiators that generate a source of free radicals whenexposed to visible radiation, are described in U.S. Pat. No. 4,735,632,which description is incorporated herein by reference. A preferred freeradical-generating initiator for use with ultraviolet light is aninitiator commercially available from Ciba Specialty Chemicals under thetrade designation “IRGACURE 651”.

Examples of useful thermal initiators, that generate a free radicalsource when exposed to thermal energy, include azo, peroxide,persulfate, and redox initiators.

Suitable azo initiators include, but are not limited to2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (VAZO 33);2,2′-azobis(2-amidinopropane)dihydrochloride ((VAZO 50);2,2′-azobis(2,4-dimethylvaleronitrile)(VAZO 52);2,2′-azobis(isobutyronitrile)(VAZO 64);2,2′-azobis-2-methylbutyronitrile (VAZO 67);1,1′-azobis(1-cyclohexanecarbonitrile)(VAZO 88), all of which areavailable from DuPont Chemicals and 2,2′-azobis(methylisobutyrate)(V-601), available from Wako Chemicals.

Suitable peroxide initiators include, but are not limited to, benzoylperoxide, acetyl peroxide, lauroyl peroxide, decanoyl peroxide, dicetylperoxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate (PERKADOX16S, available from Akzo Chemicals, Inc., di(2-ethylhexyl)peroxydicarbonate, t-butylperoxypivalate (Lupersol 11, available fromAtochem), t-butylperoxy-2-ethylhexanoate (Trigonox 21-C50, availablefrom Akzo Chemicals, Inc.), and dicumyl peroxide.

Suitable persulfate initiators include, but are not limited to,potassium persulfate, sodium persulfate, and ammonium persulfate.

Suitable redox (oxidation-reduction) initiators include, but are notlimited to, combinations of the above persulfate initiators withreducing agents such as sodium metabisulfite and sodium bisulfite;systems based on organic peroxides and tertiary amines, for example,benzoyl peroxide plus dimethylaniline; and systems based on organichydroperoxides and transition metals, for example, cumene hydroperoxideplus cobalt naphthenate.

Other initiators include, but are not limited to pinacols, such astetraphenyl 1,1,2,2-ethanediol.

Preferred thermal free-radical initiators are selected from the groupconsisting of azo compounds and peroxides. Most preferred are V-601,Lupersol 11 and Perkadox 16S, and mixtures thereof.

The initiator is present in a catalytically-effective amount and suchamounts are typically in the range of about 0.01 parts to 5 parts, andmore preferably in the range from about 0.025 to 2 parts by weight,based upon 100 total parts by weight of the total binder composition. Ifa mixture of initiators is used, the total amount of the mixture ofinitiators would be as if a single initiator was used.

Thermoplastic Polyesters

Optionally, the binder precursors of the invention may further comprisea thermoplastic polyester. Useful polyester components include bothhydroxyl and carboxyl terminated materials, which may be amorphous orsemicrystalline, of which the hydroxyl terminated materials are morepreferred. By “amorphous” is meant a material that displays a glasstransition temperature but does not display a measurable crystallinemelting point by differential scanning calorimetry (DSC). Preferably theglass transition temperature is less than the decomposition temperatureof the initiator (discussed below), but without being more than about120° C. By “semicrystalline” is meant a polyester component thatdisplays a crystalline melting point by DSC, preferably with a maximummelting point of about 150° C.

The viscosity of the polyester component is important in providing a hotmelt binder precursor composition (as opposed to a resin compositionwhich is a liquid having a measurable viscosity at room temperature).Accordingly, polyester components useful in the binder precursorcompositions of the invention preferably have a Brookfield viscositywhich exceeds 10,000 millipoise at 121° C. as measured on a BrookfieldViscometer Model #DV-II employing spindle #27 with a thermocelattachment. Viscosity is related to the molecular weight of thepolyester component. Preferred polyester components also have a numberaverage molecular weight of about 7500 to 200,000, more preferably fromabout 10,000 to 50,000 and most preferably from about 20,000 to 40,000.

Polyester components useful in the binder precursor compositions of theinvention comprise the reaction product of dicarboxylic acids (or theirdiester derivatives) and diols. The diacids (or their diesterderivatives) can be saturated aliphatic acids containing from 4 to 12carbon atoms (including unbranched, branched, or cyclic materials having5 to 6 atoms in a ring) and/or aromatic acids containing from 8 to 15carbon atoms. More specific examples of suitable polyester componentsand polyester materials are described in U.S. Pat. No. 5,436,063,incorporated herein by reference.

The components used to form the binder precursor compositions of theinvention (exclusive of additives described below) are compatible in themolten state. “Compatible” means that the molten mixture of componentsis single phased, that is, does not visibly phase separate among theindividual components and forms a homogeneous mixture of moltencomponents. Of course, one skilled in the art can easily vary theconcentrations of the epoxy resins, EVA copolymers and vinyl acetatecontent therein, optional thermoplastic polyester, and catalysts to formbinder precursor compositions of the invention without undueexperimentation. For example, one skilled in the art would generallyincrease the vinyl acetate concentration of the EVA copolymer as theconcentration of epoxy resin in the composition increases so to maintaina single phased composition in the molten state.

The specific physical properties which may be tailored to suit thespecific application by adjusting the ratio of the preceding components.Generally, increased tack and adhesion to high energy surfaces, and adecreased tendency to flow during cure is achieved by increasing therelative amount of ethylene-vinyl acetate copolymer in the composition.Increasing the relative amount of polyester in the binder compositiongenerally reduces tack, increases flow, and enhances compatibility ofthe epoxy and ethylene-vinyl acetate copolymer components. The amount ofcatalyst is selected to optimize cure speed, uncured product life, anduniformity of through cure. Thus, the relative amounts of the abovementioned ingredients are balanced depending on the properties sought inthe final cured binder.

Hydroxyl Containing Material

Optionally, the binder precursors of the invention may flirther comprisea hydroxyl-containing material. The hydroxyl-containing material may beany liquid or solid organic material having hydroxyl functionality of atleast 1, preferably at least 2. The hydroxyl-containing organic materialshould be free of other “active hydrogen” containing groups such asamino and mercapto moieties. The hydroxyl-containing organic materialshould also preferably be devoid of groups which may be thermally orphotochemically unstable so that the material will not decompose orliberate volatile components at temperatures below about 100° C. or whenexposed to an energy source during curing.

Preferably the organic material contains two or more primary orsecondary aliphatic hydroxyl groups (that is, the hydroxyl group isbonded directly to a non-aromatic carbon atom). The hydroxyl group maybe terminally situated, or may be pendant from a polymer or copolymer.The number average equivalent weight of the hydroxyl-containing materialis preferably about 31 to 2250, more preferably about 80 to 1000, andmost preferably about 80 to 350. More preferably, polyoxyalkyleneglycols and triols are used as the hydroxyl-containing material. Evenmore preferably, cyclohexane dimethanol is used as thehydroxyl-containing material.

Representative examples of suitable organic materials having a hydroxylfunctionality of 1 include allmols, monoalkyl ethers of polyoxyalkyleneglycols, and monoalkyl ethers of alkylene glycols.

Representative examples of useful monomeric polyhydroxy organicmaterials include alkylene glycols (for example, 1,2-ethanediol,1,3-propanediol, 1,4-butanediol, 2-ethyl-1,6-hexanediol, 1,4-cyclohexancdimethanol, 1,18-dihydroxyoctadecane, and 3-chloro-1,2-propanediol),polyhydroxyalkanes (for example, glycerine, trimethylolethane,pentaerythritol, and sorbitol) and other polyhydroxy compounds such asN,N-bis(hydroxyethyl)benzamide, castor oil, and the like.

Representative examples of useful polymeric hydroxyl-containingmaterials include polyoxyalkylene polyols (for example, polyoxyethyleneand polyoxypropylene glycols and triols of equivalent weight of 31 to2250 for the diols or 80 to 350 for triols), polytetra-methylene oxideglycols of varying molecular weight, hydroxyl-terminated polyesters, andhydroxyl-terminated polylactones.

Useful commercially available hydroxyl-containing materials includethose described in U.S. Pat. No. 5,436,063, incorporated herein byreference.

The amount of hydroxyl-containing organic material used in the binderprecursors of the invention may vary over a broad range, depending onfactors such as the compatibility of the hydroxyl-containing materialwith both the epoxy resin and the polyester component, the equivalentweight and functionality of the hydroxyl-containing material, and thephysical properties desired in the final cured make coat.

The optional hydroxyl-containing material is particularly useful intailoring the glass transition temperature and flexibility of the hotmelt make coats of the invention. As the equivalent weight of thehydroxyl-containing material increases, the flexibility of the hot meltmake coat correspondingly increases although there may be a consequentloss in cohesive strength. Similarly, decreasing equivalent weight mayresult in a loss of flexibility with a consequent increase in cohesivestrength. Thus, the equivalent weight of the hydroxyl-containingmaterial is selected so as to balance these two properties.

As explained more fully hereinbelow, the incorporation of polyetherpolyols into the binder precursors of the invention is especiallydesirable for adjusting the rate at which the binder precursors cureupon exposure to energy. Useful polyether polyols (that is,polyoxyalkylene polyols) for adjusting the rate of cure includepolyoxyethylene and polyoxypropylene glycols and triols having anequivalent weight of about 31 to 2250 for the diols and about 80 to 350for the triols, as well as polytetramethylene oxide glycols of varyingmolecular weight and polyoxyalkylated bisphenol A's.

The relative amount of the optional hydroxyl-containing organic materialis determined with reference to the ratio of the number of hydroxylgroups to the number of epoxy groups in the binder precursorcomposition. That ratio may range from 0:1 to 1:1, more preferably fromabout 0.4:1 to 0.8:1. Larger amounts of the hydroxyl-containing materialincrease the flexibility of the binder precursor but with a consequentloss of cohesive strength. If the hydroxyl containing material is apolyether polyol, increasing amounts will further slow the curingprocess.

Tackifiers

To improve the tack, a tackifier may be incorporated into the binderprecursor composition. This tackifier may be a rosin ester, an aromaticresin, or mixtures thereof or any other suitable tackifier.Representative examples of rosin ester tackifiers which are useful inthe present invention include glycerol rosin ester, pentaerythritolrosin ester, and hydrogenated versions of the above. Representativeexamples of aromatic resin tackifiers include alphamethyl styrene resin,styrene monomer, polystyrene, coumarone, indene, and vinyl toluene.Preferably, the tackifier is a hydrogenated rosin ester.

Useful tackifier resin types include rosin and rosin derivativesobtained from pine trees and organic acids of abietic and pimaric typewhich can be esterified, hydrogenated or polymerized (MW. to 2,000), andare commercially available from Hercules Chemical under the tradedesignation “FORALS” or from Arizona Chemical Co. as “SYLVATAC”; terpeneresins obtained from turpentine and citrus peels as alpha & beta-pineneor limonene which can be cationically polymerized (MW. 300 to 2,000) orcan be modified with C-9 monomers(terpene phenolic), and arecommercially available from Hercules Chemical under trade designation“PICCOLYTE” or from Arizona Chemical Co. under the trade designation“ZONATAC”; or certain aliphatic hydrocarbon resins such as aliphaticresins based on C-5 monomers (for example, piperylene anddicyclopentadiene) commercially available from Goodyear Chemicals underthe trade designation “WINGTACK”; aromatic resins based on C-9 monomers(for example, indene or styrene) commercially available from HerculesChemical under the trade designation “REGALREZ” or commerciallyavailable from Exxon Chemical under the trade designation “ESCOREZ2000”, which can be hydrogenated (MW 300-1200).

If a tackifier is used in the first binder precursor, it may be presentin an amount of 0.1 to 40 parts by weight, preferably 0.5 to 20 parts byweight, based on the total weight of the first binder precursor.

Size coat 20 is applied over abrasive particles 16 and make coat 18. Thesize coat may comprise a glue or a cured resinous adhesive. Examples ofsuitable resinous adhesives include phenolic, aminoplast resins havingpendant alpha, beta-unsaturated groups, urethane, acrylated urethane,epoxy, acrylated epoxy, isocyanurate, acrylated isocyanurate,urea-formaldehyde, melamine formaldehyde, bis-maleimide andfluorene-modified epoxy resins as well as mixtures thereof. Precursorsfor the size coat may further include catalysts and/or curing agents toinitiate and/or accelerate the curing process described hereinbelow. Thesize coat is selected based on the desired characteristics of thefinished coated abrasive article.

Additives and Fillers

Both the make and size coat binder precursors may additionally comprisevarious optional additives such as fillers, grinding aids, fibers,lubricants, wetting agents, surfactants, pigments, antifoaming agents,dyes, coupling agents, plasticizers and suspending agents so long asthey do not adversely affect the pressure sensitive adhesive propertiesof the make coat (before it fully cures) or detrimentally affect theability of the make or size coats to cure upon exposure to energy.Additionally, the incorporation of these additives, and the amount ofthese additives should not adversely affect the rheology of the binderprecursors. For example, the addition of too much filler can adverselyaffect processability of the make coat.

Fillers of this invention must not interfere with the adequate curing ofthe resin system in which it is contained. Examples of useful fillersfor this invention include silica such as quartz, glass beads, glassbubbles and glass fibers; silicates such as talc, clays,(montmorillonite) feldspar, mica, calcium silicate, calciummetasilicate, sodium aluminosilicate, sodium silicate; metal sulfatessuch as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodiumsulfate, aluminum sulfate; gypsum; vermiculite; wood flour; aluminumtrihydrate; carbon black; aluminum oxide; titanium dioxide; cryolite;chiolite; and metal sulfites such as calcium sulfite. Preferred fillersare feldspar and quartz.

If a grinding aid is employed in the practice of the present invention,suitable grinding aids include cryolite, chiolite, ammonium cryolite,potassium tetrafluoroborate, and the like.

Abrasive layer 14 may further comprise a third binder or supersizecoating 22. One type of useful supersize coating includes a grindingaid, such as potassium tetrafluoroborate, and an adhesive, such as anepoxy resin. This type of supersize coating is flirther described inpublished European Patent application 486,308, which is incorporatedherein by reference. Supersize coating 22 may be included to prevent orreduce the accumulation of swarf (the material abraded from a workpiece)between abrasive particles which can dramatically reduce the cuttingability of the abrasive article. Materials useful in preventing swarfaccumulation include metal salts of fatty acids (for example, zincstearate or calcium stearate), salts of phosphate esters (for example,potassium behenyl phosphate), phosphate esters, urea-formaldehyderesins, mineral oils, crosslinked silanes, crosslinked silicones,fluorochemicals and combinations thereof.

An optional back size coating 24, such as an antislip layer, comprisinga resinous adhesive having filler particles dispersed therein can beprovided. Alternatively, the backsize coating may be a pressuresensitive adhesive for bonding the coated abrasive article to a supportpad may be provided on backing 12. Examples of suitable pressuresensitive adhesives include latex, crepe, rosin, acrylate polymers (forexample, polybutyl acrylate and polyacrylate esters), acrylatecopolymers (for example, isooctylacrylate/acrylic acid), vinyl ethers(for example, polyvinyl n-butyl ether), alkyd adhesives, rubberadhesives (for example, natural rubbers, synthetic rubbers andchlorinated rubbers), and mixtures thereof. An example of a pressuresensitive adhesive coating is described in U.S. Pat. No. 5,520,957,incorporated herein by reference.

The back size coating may also contain an electrically conductivematerial such as vanadium pentoxide (in, for example, a sulfonatedpolyester), or carbon black or graphite in a binder. Examples of usefulconductive back size coatings are disclosed in U.S Pat. No. 5,108,463and U.S. Pat. No. 5,137,452, both of which are incorporated herein byreference.

In order to promote the adhesion of make coat 18 and/or back sizecoating 24 (if included), it may be necessary to modify the surface towhich these layers are applied. For example, if a polymeric film is usedas the backing, it may be preferred to modify the surface of, that is,“prime”, the film. Appropriate surface modifications include coronadischarge, ultraviolet light exposure, electron beam exposure, flamedischarge and scuffing.

Methods of Making

The following section will describe exemplary means on how to make theabrasive articles of the invention, especially with respect to mannersof forming the abrasive surface thereof.

The first binder precursor may be prepared by mixing the variousingredients in a suitable vessel at an elevated temperature sufficientto liquify the materials so that they may be efficiently mixed withstirring but without thermally degrading them until the components arethoroughly melt blended. This temperature depends in part upon theparticular chemistry. For example, this temperature may range from about30 to 150° C., typically 50 to 130° C., and preferably ranges from 60 to120° C. The components may be added simultaneously or sequentially,although it is preferred to first blend the ethylene-vinyl acetatecopolymer and the solid epoxy resin, in order, followed by the additionof the liquid epoxy resin, a polyfunctional acrylate component (ifpresent) and any optional hydroxyl-containing material. Then, thecatalysts (photoinitiator, photocatalyst, and/or thermal catalyst) areadded followed by any optional additives including fillers or grindingaids.

The binder precursor should be compatible in the uncured, melt phase.That is, there should preferably be no visible gross phase separationamong the components before curing is initiated. The binder precursormay be used directly after melt blending or may be packaged in pails,drums or other suitable containers, preferably in the absence of light,until ready for use. The binder precursor so packaged may be deliveredto a hot-melt applicator system with the use of pail unloaders and thelike. Alternatively, the uncured binder precursors of the invention maybe delivered to conventional bulk hot melt applicator and dispensersystems in the form of sticks, pellets, slugs, blocks, pillows orbillets. It is also feasible to incorporate organic solvent into thebinder precursor; although this may not always be preferred.

It is also possible to provide the first binder precursors of theinvention as uncured, unsupported rolls of tacky, pressure sensitiveadhesive film. In this instance, the binder precursor is extruded, cast,or coated to form the film. Such films are useful in transfer coatingthe first binder precursor to an abrasive article backing. It isdesirable to roll up the tacky film with a release liner (for example,silicone-coated Kraft paper), with subsequent packaging in a bag orother container that is not transparent to actinic radiation.

The first binder precursors of the invention may be applied to theabrasive article backing by extrusion, gravure printing, coating, (forexample, by using a coating die, a heated knife blade coater, a rollcoater, a curtain coater, or a reverse roll coater), or transfer coater.When applying by any of these methods, it is preferred that the makecoat be applied at a temperature of about 50 to 125° C. more preferablyfrom about 80 to 125° C.

The binder precursors of the invention can be supplied as free standing,unsupported pressure sensitive adhesive films that can be transfercoated to the backing and, if necessary, die cut to a predefined shapebefore transfer coating. Transfer coating temperatures and pressures areselected so as to minimize both degradation of the backing and bleedthrough of the make coat and may range from room temperature to about120° C. and about 30 to 250 psi (2.1 to 17.8 kg/cm²). A typical profileis to transfer coat at room temperature and 100 psi (7.0 kg/cm²).Transfer coating is a particularly preferred application method for usewith highly porous backings.

It is also within the scope of this invention to coat the make coat orbinder precursor as a liquid, as from a solvent, although this method isnot preferred. A liquid binder precursor can be applied to the backingby any conventional technique such as roll coating, spray coating, diecoating, knife coating, and the like. After coating the resultinguncured make coat, it may be exposed to an energy source to activate thecatalyst before the abrasive grains are embedded into the make coat.Alternatively, the abrasive grains may be coated immediately after themake coat binder precursor is coated before partial cure is effected.

The coating weight of the make coat or binder precursor of the inventionapplied to a backing can vary depending on the grade of the abrasiveparticles to be used. For instance, finer grade abrasive particles willgenerally require less make coat to bond the abrasive particles to thebacking. Sufficient amounts of binder precursor must be provided tosatisfactorily bond the abrasive particles. However, if the amount ofbinder precursor applied is too great, the abrasive particles may becomepartially or totally submerged in the make coating, which isundesirable. In general, the application rate of the binder precursorcomposition of this invention (on a solvent free basis) is between about4 to 300 g/m², preferably between about 20 to about 30 g/m².

Preferably, the make coat binder precursor is applied to the abrasivearticle backing by any of the methods described above, and once soapplied is exposed to an energy source to initiate at least partial cureof the epoxy resin and the polyfunctional acrylate component, ifpresent. Curing of the make coat binder precursor begins upon exposureof the binder precursor to an appropriate energy source and continuesfor a period of time thereafter. The energy source is selected for thedesired processing conditions and to appropriately activate the epoxycatalyst. The energy may be actinic (for example, radiation having awavelength in the ultraviolet or visible region of the spectrum),accelerated particles (for example, electron beam radiation), or thermal(for example, heat or infrared radiation). Preferably, the energy isactinic radiation (that is, radiation having a wavelength in theultraviolet or visible spectral regions). Suitable sources of actinicradiation include mercury, xenon, carbon arc, tungsten filament lamps,sunlight, and so forth.

Ultraviolet radiation, especially from a medium pressure mercury arclamp, is most preferred. Exposure times may be from less than about 1second to 10 minutes or more (to preferably provide a total energyexposure from about 0.1 to about 10 Joule/square centimeter (J/cm²))depending upon both the amount and the type of reactants involved, theenergy source, web speed, the distance from the energy source, and thethickness of the make coat to be cured.

The binder precursors of the invention may also be cured by exposure toelectron beam radiation. The dosage necessary is generally from lessthan 1 megarad to 100 megarads or more. The rate of curing may tend toincrease with increasing amounts of photocatalyst and/or photoinitiatorat a given energy exposure or by use of electron beam energy with nophotoinitiator. The rate of curing also may tend to increase withincreased energy intensity.

Use of the cationic organometallic salt as epoxy photocatalyst allowsdelayed cure, even in the absence of polyols, which enables the binderprecursor to retain its pressure sensitive properties for a timesufficient to permit abrasive particles to be adhered thereto after thebinder precursor has been exposed to the energy source.

The abrasive particles may be applied until the make coat binderprecursor has sufficiently cured that the particles will no longeradhere, although to increase the speed of a commercial manufacturingoperation, it is desirable to apply the abrasive particles as soon aspossible, typically within a few seconds of the make coat binderprecursor having been exposed to the energy source. The abrasiveparticles can be applied by drop coating, preferably, electrostaticcoating, or magnetic coating according to conventional techniques in thefield. An example of a process that may be used to make the abrasivearticles of the invention can be found in U.S. application Ser. No.08/710,596, entitled “Coated Abrasive Article,” filed Sep. 20, 1996, nowU.S. Pat. No. 5,766,277 incorporated herein by reference.

The time to reach fall cure may be accelerated by post curing of themake coat with heat, such as in an oven. Post curing can also affect thephysical properties of the make coat and is generally desirable. Thetime and temperature of the post cure will vary depending upon the glasstransition temperature of the ethylene-vinyl acetate copolymer, theconcentration of the initiator, the energy exposure conditions, and thelike. Post cure conditions can range from less than a few seconds at atemperature of about 150° C. to longer times at lower temperatures.Typical post cure conditions are about one minute or less at atemperature of about 100° C.

In an alternative manufacturing approach, the make coat binder precursoris applied to the backing and the abrasive particles are then projectedinto the make coat binder precursor followed by exposure of the makecoat binder precursor to an energy source.

Size coat 20 may be subsequently applied over the abrasive particles andthe make coat as a flowable liquid by a variety of techniques such asroll coating, spray coating, gravure coating, or curtain coating and canbe subsequently cured by drying, heating, or with electron beam orultraviolet light radiation. The particular curing approach may varydepending on the chemistry of the size coat. Optional supersize coating22 may be applied and cured or dried in a similar manner.

Optional back size coating 24 may be applied to backing 12 using any ofa variety of conventional coating techniques such as dip coating, rollcoating, spraying, Meyer bar, doctor blade, curtain coating, gravureprinting, thermomass transfer, flexographic printing, screen printing,and the like.

In an alternate backing arrangement, the back side of the abrasivearticle may contain a loop substrate. The purpose of the loop substrateis to provide a means that the abrasive article can be securely engagedwith hooks from a support pad. The loop substrate may be laminated tothe coated abrasive backing by any conventional means. The loopsubstrate may be laminated prior to the application of the make coatprecursor or alternatively, the loop substrate may be laminated afterthe application of the make coat precursor.

In another aspect, the loop substrate may in essence be the coatedabrasive backing. The loop substrate will generally comprise a planarsurface with the loops projecting from the back side of the front sideof the planar surface. The make coat precursor is coated on this planarsurface. In this aspect, the make coat precursor is directly coated ontothe planar surface of the loop substrate. In some instances, the loopsubstrate may contain a presize coating over the planar surface whichseals the loop substrate. This presize coating may be a thermosettingpolymer or a thermoplastic polymer. Alternatively, the make coatprecursor may be directly coated onto the non-looped side of an unsealedloop substrate. The loop substrate may be a chenille stitched loop, anextruded bonded loop, a stitchbonded loop substrate or a brushed loopsubstrate (for example, brushed polyester or nylon). Examples of typicalloop backings are further described in U.S. Pat. Nos. 4,609,581 and5,254,194, both of which are incorporated herein by reference.

The loop substrate may also contain a sealing coat over the planarsurface to seal the loop substrate and prevent the make coat precursorfrom penetrating into the loop substrate. Additionally, the loopsubstrate may comprise a thermoplastic sealing coat and projecting fromthe thermoplastic sealing are a plurality of corrugated fibers. Thisplurality of corrugated fibers actually forms a sheet of fibers. It ispreferred that these fibers have arcuate portions projecting in the samedirection from spaced anchor portions. In some instances, it ispreferred to coat directly onto the planar surface of the loop substrateto avoid the cost associated with a conventional backing. The make coatbinder precursor can be formulated and coated such that the make coatprecursor does not significantly penetrate into the loop substrate. Thisresults in a sufficient amount of make coat precursor to securely bondthe abrasive particles to the loop substrate.

Likewise, the back side of the abrasive article may contain a pluralityof hooks; these hooks are typically in the form of sheet like substratehaving a plurality of hooks protruding from the back side of thesubstrate. These hooks will then provide the means of engagement betweenthe coated abrasive article and a support pad that contains a loopfabric. This hooked substrate may be laminated to the coated abrasivebacking by any conventional means. The hooked substrate may be laminatedprior to the application of the make coat precursor or alternatively,the hooked substrate may be laminated atfer the application of the makecoat precursor. In another aspect, the hooked substrate may in essencebe the coated abrasive backing. In this scenario, the make coatprecursor is directly coated onto the hooked substrate. In someinstances, it is preferred to coat directly onto a hooked substrate toavoid the cost associated with a conventional backing. Additionaldetails on the use of hooked backings or lamination of hooks can befound in U.S. Pat. No. 5,505,747 (Chesley et al.), incorporated hereinby reference.

The binder precursors of the invention provide a balance of highlydesirable properties. As solvent free formulations, they are easilyapplied using conventional hot melt dispensing systems. Consequently,they can be supplied as pressure sensitive adhesive films well suitedfor lamination to a backing. The inclusion of an ethylene-vinyl acetatecopolymer provides the binder precursors with pressure sensitiveproperties which facilitates the application of the abrasive particlesthereto. The provision of a polyether polyol of appropriate molecularweight and functionality provides the make coats of the invention withan open time subsequent to energy exposure that permits the abrasiveparticles to be projected into the binder precursor after it has beenexposed to energy. The incorporation of a polyfunctional acrylatecomponent in the make coat provides superior rheology control.

More specifically, the binder precursor formulations used in the presentinvention have a lower cost, longer open time, and better film-formingproperties than make resins containing only epoxy and thermoplasticpolyester. As a result of the enhanced film forming properties, thebinder compositions of the present invention require less thermoplasticin the formulation, futrther reducing cost and improving theelevated-temperature properties of the material.

The invention will be more fully understood with reference to thefollowing nonlimiting examples in which all parts, percentages, ratios,and so forth, are by weight unless otherwise indicated.

Abbreviations used in the examples have the definitions shown in thefollowing schedule.

DS1227 a high molecular weight polyester under the trade designation“DYNAPOL S1227” commercially available from Creanova, Piscataway, NJDS1402 a high molecular weight polyester with low crystallinity underthe trade designation “DYNAPOL S1402” commercially available fromCreanova, Piscataway, NJ EL 310 an ethylene-vinyl acetate copolymer (25%vinyl acetate) commercially available from E. I. Du Pont de Nemours andCo. (Wilmington, DE) under the trade designation “ELVAX 310” EL 220 anethylene-vinyl acetate copolymer (28% vinyl acetate) commerciallyavailable from E. I. Du Pont de Nemours and Co. (Wilmington, DE) underthe trade designation “ELVAX 220” EL 140 an ethylene-vinyl acetatecopolymer (33% vinyl acetate) commercially available from E. I. Du Pontde Nemours and Co. (Wilmington, DE) under the trade designation “ELVAX140” L700 an ethylene-vinyl acetate copolymer commercially availablefrom Bayer Corp. (Pittsburgh, PA) under the trade designation “LEVAPREN700” E828 a bisphenol A epoxy resin under the trade designation “EPON828” (epoxy equivalent wt. of 185-192 g/eq) commercially available fromShell Chemical, Houston, TX E1001 a bisphenol A epoxy resin under thetrade designation “EPON 1001F” (epoxy equivalent wt. of 525-550 g/eq)commercially available from Shell Chemical, Houston, TX E4221 acycloaliphatic epoxy resin under the trade designation “ERL 4221 (epoxyequivalent wt. of 126 g/eq) commercially available from Union CarbideCorp., Danbury, CT CHDM cyclohexanedimethanol TMPTA trimethylol propanetriacrylate commercially available from Sartomer Co., Exton, PA underthe trade designation “SR351” KB1 2,2-dimethoxy-1,2-diphenyl-1-ethanonecommercially available from Ciba Specialty Chemicals under the tradedesignation “IRGACURE 651” or commercially available from Sartomer Co.,Exton, PA under the trade designation “KB1” per se COM η⁵-[xylenes(mixed isomers)]eta⁵-cyclopentadienyliron(1+) hexafluoroantimonate (1−)(acts as a catalyst) AMOX di-t-amyloxalate (acts as an accelerator) CRYcryolite AO fused aluminum oxide HTAO heat treated fiised aluminum oxide

TEST PROCEDURES

The Examples and Comparative Examples described below were testedaccording to the following test procedure.

TEST #1: Schiefer Test Procedure

The coated abrasive article for each example was converted into a 10.2cm diameter disc and secured to a foam back-up pad by means of apressure sensitive adhesive. The coated abrasive disc and back-up padassembly was installed on a SCHIEFER testing machine, and the coatedabrasive disc was used to abrade a donut shaped cellulose acetatebutyrate polymer or 1018 mild steel workpiece. The load was 4.5 kg. Theendpoint of the test was 500 revolutions or cycles of the coatedabrasive disc. The amount of cellulose acetate butyrate polymer removedwas measured at the end of the test. The mineral pick-up achieved andcut determined by TEST #1 for each example, are summarized in the databelow.

Melt Blending to Form Eva/Epoxy Blends

Two hundred gram samples were prepared by melting the EVA copolymer in aone quart paint can at 100-150° C. adding liquid epoxy (if E1001 isadded, it is melted first), blending with an air mixer, adding remainderof the liquid epoxy and cyclohexanedimethanol (CHDM) if present (2.4% oftotal in all examples in which it was used), blending again, reducingthe temperature to 100-120° C., and adding CpFeXylenes⁺ SbF₆ ⁻ (COM) anddi-tert-amyl oxalate (AMOX), 0.6-1% each. Resins were coated ontorelease liner (silicone release on PET film) using a hot knife at95-100° C., 0.05-0.10 mm thick. Thicker samples were used for physicalproperty testing (DMA and DSC). Thinner coatings 0.05 mm were laminatedonto abrasives backings, including 36×34 threads/cm polycotton forutility cloth products, a stem web substrate, and a variety of paperbackings. All make resins containing EVA copolymer were melt blendedexcept those containing L700.

Solvent Blending to Form Eva/Epoxy Blends

L700 was dissolved in ethyl acetate or methyl ethyl ketone at 25-40%solids, epoxy and CHDM (if present) added, and solvent stripped offunder vacuum at 60-90° C. Photocatalyst system was added (adding COM andAMOX, 0.6-1% each) to the melt at 100-120° C., mixed with air mixer, andcoated onto a substrate as described above. Solvent blending of thebinder resins of the invention is not preferred, however, the measuredphysical properties of solvent blended and melt blended binders areexpected to be within experimental error.

The preferred method of blending the binder resins containing highervinyl acetate EVA copolymers is as follows: EVA copolymer pellets werefed into a co-rotating intermeshing twin screw extruder and meltedbetween a temperature of 80 and 140° C. Solid epoxy resin (E1001) flakeswere melted and pumped as a liquid into a port downstream of thethermoplastic. Finally, all other components (E828, COM, AMOX, andoptionally CHDM, TMTPA, and KB1) were mixed at a temperature of 75° C.in a batch process. The resulting homogenous liquid was pumped into anextruder downstream of the solid epoxy and thermoplastic. The extrudatewas collected in silicone-lined boxes and stored as a solid at roomtemperature in the dark. In this form it was conveniently remelted asneeded for further use.

Dynamic Mechanical Analysis (DMA)

Samples were prepared by coating curable hot melt between two polyesterrelease liners, 2-5 mils thick. Coatings were exposed to approximately 3J/cm2 of radiant energy from TLD 15W/03 bulbs (Philips B. V., Holland)through release liners. Exposed samples were then placed in an oven at100-110° C. for 30 min to ensure cure. Strips of cured film were cut 1.0cm wide, approximately 2-3 cm long. A Seiko Instruments DMA 200Rheometer (Seiko Instruments, Torrance, Calif.) equipped with a tensilesample fixture was used. Separation of the jaws was 10 mm. Thetemperature ramp was 2 degrees per minute from −80 to 250° C., at asingle frequency of 1 Hz. DMA data are displayed in Tables 1-3.

TABLE 1 Material Properties of EVA/Epoxy Melt processable Resins % VinylDMA DMA Acetate DMA E′ (25° C., E′ (100° C., Formulation in EVA T_(g)(°C.) MPa) Mpa) 40% EVA 25 −30° C./134 700 300 (EL310) 60% Epoxy 40% EVA28 −31° C./125 130 60 (EL220) 60% Epoxy 40% EVA 33 −28° C./116 80 20 (EL140) 60% Epoxy 10% EVA 70  −3° C./150 700 300 (L700) 90% Epoxy (E828) NoCHDM 20%EVA 70  53° C./125 1000 130 (L700) 80% Epoxy (E828) No CHDM 10%EVA 70 110 2100 400 (L700) 90% Epoxy (E1001) No CHDM 20% EVA 70 117 1300400 (L700) 80% Epoxy (E 1001) No CHDM

TABLE 2 Material Properties of Melt Processable EVA/Epoxy Blends % VinylDMA DMA Acetate DMA E′ (25° C., E′ (100° C., Formulation in EVA T_(g)(°C.) MPa) Mpa) 10% EVA 70 99 1600 30 (L700) 90% Epoxy (E 1001) CHDM 15%EVA 70 101 1400 60 (L700) 85% Epoxy (E 1001) CHDM 20% EVA 70 97 1100 20(L700) 80% Epoxy (E 1001) CHDM 25% EVA 70 102 1100 60 (L700) 75% Epoxy(E 1001) CHDM

TABLE 3 Material Properties of EVA/Epoxy Blends; Effects of CryoliteFiller. % Vinyl DMA DMA Acetate DMA E′ (25° C., E′ (100° C., Formulationin EVA T_(g)(° C.) MPa) MPa) 15% EVA 70 138 1000 600 (L700) 85% Epoxy(6:4 E1001:E828) No CHDM 12% EVA 70 138 1800 860 (L700) 68% Epoxy (6:4E1001:E828) No CHDM 20% Cryolite 12% EVA 70 97 1400 750 (L700) 68% Epoxy(6:4 E1061:E828) CHDM 20% Cryolite 15% EVA 70 123 520 290 (L700) 85%Epoxy (6:4 E1001:E828) CHDM

The physical properties of the EVA/epoxy blends show that the mostcompatible blends are those containing EVA copolymers having vinylacetate content near 70% by weight. Preferred compositions for abrasiveapplications are those compositions containing EVA copolymers havingvinyl acetate content of about 60-80% by weight, an EVA copolymerconcentration in the range of 10-20% by weight relative to epoxy resin,and no chain extender (CHDM). These materials have Knoop Hardness (KHN)values of about ten, comparable to that of epoxy/polyester/polyacrylatemelt processable resin systems. The addition of fillers is alsopossible; the use of cryolite is illustrated in Table 3. Preferredbinder compositions have glass transition temperatures (T_(g)'s) wellover 60° C. after curing, for best abrasive performance.

Preparation of Comparative Example a and Example 1

Comparative Example A was “3M Grade P180 216U Production Fre-Cut AWeight Paper”, commercially available from Minnesota Mining andManufacturing Company of St. Paul, Minn. Example 1 comprised an abrasiveconstruction having a 115 g/m² paper backing from Kammerer GmbH,(Osnabruck, Germany), an EVA/epoxy blend make coat (15% L700, 85% E1001,0.6% COM, and 0.6% AMOX), P180 AO applied electrostatically into themake coat, a radiation-curable size coat (60% E828, 20% E4221, 20% DIPT,and 1.0% COM), and a zinc stearate supersize as described in U.S. Pat.No. 5,611,825 as “A3469”, incorporated by reference herein.Representative (typical) coating weights for Example 1 were: makeweight=100 g/m²; mineral weight=120 g/m²; size weight=50 g/m²; supersizeweight=25 g/m²

The Schiefer cut results were:

SCHIEFER CUT EXAMPLE (g/500 cycles) Comparative Example A 2.78 Example 13.14

The cut performance of Example 1 is approximately 13% better than thatof Comparative Example A.

Preparation of Comparative Examples B and C and Examples 2 and 3

Comparative examples B and C were blended at a temperature of 140° C.The acrylate and epoxy catalysts and the photoinitiator, were added intothe molten mixture and blended just before coating. Examples 2 and 3were solvent blended (not preferred); the epoxy resins and the EVAcopolymer were dissolved in methyl ethyl ketone. The solvent wasgradually removed in a vacuum oven while the temperature was raised to120° C. After 30 minutes at a temperature of 120° C. and a vacuum of 1.0Torr, it was assumed that all of the solvent had been removed. Thesamples were moved to a conventional oven and the rest of the componentswere added as in Comparative Examples B and C. Preferably, the samplesare melt blended as described above. The compositions (parts by weight)are described in Table 4.

Approximately 0.08 mm thick coatings were knife coated onto a paperbacking (150 g/m² from UPM-Kymmene, Pietarsaari, Finland), with both theknife and coating bed at a temperature of approximately 130° C.Additional samples of Examples 2 and 3 were coated onto asilicone-treated polyester release liner and transfer coated at roomtemperature to the same paper backing. No difference was seen in eitherthe mineral coating or product performance between the samples coateddirectly onto the backing and those which had been transfer coated. Themake coat weight for each sample was approximately 75 g/m².

The coatings were irradiated with a 236 Watt/cm Fusion Systems “D” bulbat a web speed of 15 m/min. The irradiated coatings were thenelectrostatically coated with grade P80 HTAO mineral. The make resin wasthen heated at 120° C. for 10 minutes to finally cure the resin.

A size resin containing 40% E828, 30% E4221, 30% TMPTA, 1% KB1 and 1%COM was dispersed in methyl ethyl ketone and brushed onto the samples atan approximate weight of 120 g/m² (dry weight). These coated sampleswere irradiated by a 236 W/cm Fusion “D” bulb at 15 m/min, and cured for10 minutes at 120° C.

Table 5 shows the grade P80 mineral coating weights and the SchieferTest performance results of the above Examples and Comparative Examples.

TABLE 4 Comparative Comparative Example Example Formulation B C 2 3 DS1227 (pbw) 28 21 0 0 L 700 (pbw) 0 0 28 21 E 828 (pbw) 37 41 39 43 E1001 (pbw) 26 29 27 30 CHDM(pbw) 3 3 0 0 TMTPA (pbw) 3.8 3.8 3.8 3.8 KB1(pbw) 1 1 1 1 COM (pbw) 0.6 0.6 0.6 0.6 AMOX (pbw) 0.6 0.6 0.6 0.6

TABLE 4 Comparative Comparative Example Example Formulation B C 2 3 DS1227 (pbw) 28 21 0 0 L 700 (pbw) 0 0 28 21 E 828 (pbw) 37 41 39 43 E1001 (pbw) 26 29 27 30 CHDM(pbw) 3 3 0 0 TMTPA (pbw) 3.8 3.8 3.8 3.8 KB1(pbw) 1 1 1 1 COM (pbw) 0.6 0.6 0.6 0.6 AMOX (pbw) 0.6 0.6 0.6 0.6

The data in Table 5 indicate that the make resin systems of bothExamples 2 and 3 more readily accept mineral particles than the makeresin systems of both Comparative Examples B and C. The make resinsystems of Examples 2 and 3 likely have more tackiness over an extendedtime window due to the lower rate of crystallization than the make resinsystems of Comparative Examples B and C.

The Schiefer test is known as both a sharpness (mineral orientation) andan antiloading test. Since antiloading is known to be enhanced byperipheral antiloading additives (not present here), mineralorientation, and open coated constructions, that is, those with about20-30% less abrasive particle (mineral) concentration, Examples 2 and 3having higher mineral or abrasive particle coatings would not beexpected to perform better than Comparative Examples B and C.

By comparison, the results of the mild steel Schiefer test indicate thatall four constructions perform similarly (adequately) and appearunaffected by both the concentration (amount) of mineral present and thetype of make coat composition.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrated embodiment setforth herein.

What is claimed is:
 1. A method of preparing a coated abrasive article,comprising the steps of: (a) providing a backing having a front surfaceand a back surface; (b) applying to said front surface of said backingan energy-curable, melt processable first binder precursor, wherein saidfirst binder precursor comprises: i) an epoxy resin, ii) a thermoplasticconsisting essentially of an ethylene-vinyl acetate, and iii) a curngagent for crosslinitng said epoxy resin; (c) exposing said first binderprecursor to an energy source to initiate at least partial curing ofsaid first binder precursor; (d) at least partially embedding aplurality of abrasive particles in said first binder precursor; and (e)permitting said first binder precursor to sufficiently cure to form acrosslinked coating with said abrasive particles at least partiallyembedded therein.